The present invention relates to a semiconductor optical device and, more particularly, to a semiconductor optical device suitable for use as a light-emitting diode or a laser for coherent optical communications.
In order to improve directionality and wavelength selectivity of light in the light-emitting semiconductor device, i.e., the light-emitting diode and laser, a distributed feedback semiconductor laser has been proposed. There has also been proposed a so-called micro-cavity laser as a semiconductor laser provided in an extremely small structure. For example, in a micro-cavity laser having a structure comparable to a wavelength, as described in Extended abstracts (the 43rd Autumn Meeting (1982)), the Japan Society of Applied Physics, and related Society, 29a-B-6, p. 127, all of the light waves are regulated by eigen (resonant) modes of extremely small number (several or zero), not only induced transition but also spontaneous emission process is extremely limited, and therefore, it becomes possible to realize novel optical devices such as coherent light-emitting devices or coherent LEDs with no threshold value and lasers with a very low threshold value.
However, since the above distributed feedback semiconductor laser requires that a grating is formed on the semiconductor substrate, crystalline defects are liable to be produced at the time of crystal growth. There have therefore been such drawbacks with it that a semiconductor laser of high quality is difficult to obtain. Further, since the micro-cavity laser requires a very high level of techniques in its fabrication, it has been very difficult to actually produce lasers having uniform characteristics with good reproducibility.
An object of the present invention is to eliminate the drawbacks in the above described distributed feedback semiconductor laser and to provide a semiconductor optical device with high directionality and wavelength selectivity of light.
Another object of the present invention is to provide a micro-cavity laser which can be manufactured easily and with good reproducibility.